Numerous reports indicate that the thiol:protein disulfide oxidoreductase plays an important role in insulin degradation. This proposal will extend our current mechanistic understanding of the enzyme. The two forms of the enzyme will be characterized using protein biochemistry, amino acid sequence analysis and affinity-labeling of the enzyme. The hormonal regulation of the thiol:protein disulfide oxidoreductase will be examined in isolated hepatocytes and liver slices. The mechanism of hormonal regulation will also be determined. A better understanding of the molecular events associated with insulin degradation will undoubtedly provide us with a more complete picture of the molecular aspects of diabetes mellitus. In addition, this proposal will seek to determine the factors responsible for the regulating the N-terminal acetylation of proteins and hormones. Model peptides will be used as substrates for the purification and characterization of the N-alpha-acetyltransferases. The two specific systems which will be examined are: (a) N-alpha-acetylation of ACTH and fragments of the hormone using a rat pituitary N-alpha-acetyltransferase and (b) the peptide corresponding to the first ten amino acids of ovalbumin and the hen oviduct N-alpha-acetyltransferase.